Multiple speed motor with thermal overload protection

ABSTRACT

An electric motor includes a stator and a rotor. The stator has a plurality of low speed windings and a plurality of separate high speed windings. A first type of thermal overload protector is coupled with at least one of the low speed windings and a second type of thermal overload protector is coupled with at least one of the high speed windings.

BACKGROUND

Electric motors commonly include a stationary component called a statorand a rotating component called a rotor. The stator has a number ofwindings, and the rotor rotates within (or around) the stator when thestator windings are energized with a driving waveform. Electric motorsare used in a variety of applications including HVAC systems,appliances, etc.

Electric motors sometimes fail prematurely. Motor failures interrupt theoperation of the systems in which they are used and can causesignificant economic losses and safety problems. Many motor failures arerelated to excessive heat. A motor can overheat due to a variety offactors including a locked rotor, low line voltage, starting overload,running overload, poor motor ventilation, and/or abnormally high ambienttemperatures. Such overheating can damage the insulation on the statorwindings, which reduces motor life and can even result in complete motorfailure and fires.

Most motors are therefore equipped with thermal overload protectiondevices that cut off electricity to the motors when motor temperaturesexceed a maximum safe level. Many different overload protection deviceshave been developed including: current sensitive devices such as circuitbreakers, fuses, etc. that are typically mounted external to motors andsense current overloads; combination current and temperature sensitivedevices such as thermal disc type protectors that are often mounted inmotor casings; and temperature sensitive devices that are wired directlyto motor windings to directly sense motor winding temperatures.

Governmental and/or regulatory entities have stiffened the efficiencyrequirements of HVAC systems and other electrical systems withmultispeed motors. Such motors typically have two or more sets of statorwindings to provide two or more motor speeds. For safety reasons, whenindependent stator windings are used for different motor speeds, eachset must be separately protected against thermal overloads.

SUMMARY

Applicant has discovered that equipping multi-speed motors with thermaloverload protection devices for all stator windings can be difficult fora variety of issues. For example, although thermal disc type protectorsprovide excellent protection against thermal overloads, many motorcasings are not large enough to accommodate a separate protector foreach motor speed.

Embodiments of the present invention solve the above described problemsby providing improved techniques for protecting multispeed electricmotors against thermal overloads. A motor constructed in accordance withan embodiment of the present invention may be used in a washing machine,HVAC system, pump system or any other application and broadly comprisesa stator and a rotor. The stator has a plurality of low speed windingsand a plurality of separate high speed windings. A first type of thermaloverload protector is coupled with at least one of the low speedwindings and a second different type of thermal overload protector iscoupled with at least one of the high speed windings.

In one embodiment, the first type of thermal overload protector is arelatively small and inexpensive on-winding thermal protector, and thesecond type of thermal overload protector is a relatively larger andmore costly phenolic disc type protector. Applicant has discovered thatthe current on the low speed stator windings is low enough to permit useof the on-winding type protector, whereas the current on the high speedstator windings necessitates use of the phenolic disc type protector. Byusing two distinct types of thermal overload protectors, the shell orcasing of the motor can be smaller because it only has to accommodateone phenolic disc type protector. The present invention also reduces theoverall cost of the motor because a less expensive on-winding protectoris used for the low speed windings.

This summary is provided to introduce a selection of concepts in asimplified form that are further described in the detailed descriptionbelow. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the present invention will be apparent from thefollowing detailed description of the embodiments and the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a block diagram of a motor assembly constructed in accordancewith an embodiment of the invention.

FIG. 2 is a schematic representation of the stator and rotor of themotor shown in FIG. 1.

FIG. 3 is a schematic diagram of the low speed stator windings of theelectric motor.

FIG. 4 is a schematic diagram of the high speed stator windings of theelectric motor.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying drawings. The embodiments are intended todescribe aspects of the invention in sufficient detail to enable thoseskilled in the art to practice the invention. Other embodiments can beutilized and changes can be made without departing from the scope of theclaims. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the present technology can include a variety of combinationsand/or integrations of the embodiments described herein.

Turning now to the drawing figures, and initially FIG. 1, a motorassembly 10 constructed in accordance with embodiments of the inventionis illustrated. The motor assembly 10 may be used in any application,such as in a washing machine, HVAC system, pump system, or appliance. Inone embodiment, the motor assembly 10 is designed for use in a blowerassembly of an HVAC system, but the principles of the present inventionare equally applicable to all uses of the motor assembly.

An embodiment of the motor assembly 10 broadly includes an electricmotor 12 and a motor controller 14. The motor assembly 10 may alsoinclude or be coupled with other systems or components not relevant tothe present invention.

As best illustrated in FIG. 2, the electric motor 12 includes a rotor 16and a stator 18. The motor 12 may operate on direct current (DC) oralternating current (AC), may be synchronous or asynchronous, and may besingle phase or three phase. The motor 12 may be of any type, includingbut not limited to, a brushed or brushless DC motor, a coreless orironless DC motor, a series wound universal motor, an induction motor, atorque motor, or a stepper motor. Moreover, the motor may have anyvoltage and horsepower (HP) rating.

To provide for multi-speed operation, an embodiment of the stator 18includes a number of low speed windings 20 and a number of independenthigh speed windings 22 as shown in FIGS. 3 and 4. The low speed windings20 and high speed windings 22 are powered by separate motor leads sothat the two motor speeds are on separate circuits. For example, themotor 12 may include a three phase power input that provides independentthree phase power to the low and high speed windings. In one embodiment,the motor includes 6-pole low speed windings as shown in FIGS. 3 and4-pole high speed windings as shown in FIG. 4.

In one particular embodiment of the invention, the motor 12 is a threephase, 36 slot, multi-speed, induction motor that is rated 0.75/0.33 HPat 208-230 Volts, 1/0.44 HP at 460 Volts, and 2/0.89 HP at 575 Volts.However, the principles of the present invention are not limited to anyparticular motor type, technology, or size.

The motor also has a motor casing, housing, or shell 24 that at leastpartially encloses and protects the stator 18 and the rotor 16. Themotor shell 24 has an end shield in which wiring and electricalcomponents of the motor assembly are mounted as described below.

In accordance with one important aspect of the invention, a low speedwinding thermal overload protector 26 is coupled with the low speedwindings as shown in FIG. 3 and a high speed winding thermal overloadprotector 28 is coupled with the high speed windings as shown in FIG. 4.The low speed winding and high speed winding thermal overload protectorsare electrically isolated from one another to provide independentprotection of the low and high speed windings. In some embodiments, thelow speed winding thermal overload protector 26 and the high speedwinding thermal overload protector 28 may be different types. In otherembodiments, the low speed winding thermal overload protector 26 and thehigh speed winding thermal overload protector 28 may be the same type.

One type of protector that may be used with both the low speed windingthermal overload protector 26 and the high speed winding thermaloverload protector 28 is an on-winding thermal overload protector. Inone implementation, two on-winding protectors are used with oneon-winding protector connected to each of the windings of two phases, asshown for example with the low-speed stator windings 20 in FIG. 3. Inother implementations, three on-winding protectors are provided suchthat the windings of all three phases are protected. An exemplary typeof on-winding thermal overload protector may be Klixon® 7 AM seriesthermal protectors. Other series or families of thermal protectors fromKlixon® may be used as well as thermal protectors from othermanufacturers or vendors. The 7 AM protectors are thermally operatedsnap action devices with miniature bimetal snap-action contacts throughwhich current flows. If the windings to which the protectors areconnected overheat for any of the reasons discussed above, the heatingeffect of the current flow through the contacts causes the contacts'temperatures to rise. When the contacts' temperatures reaches theircalibrated set point temperature, they snap open and disconnect thecurrent to the stator windings. When the windings and hence the contactsof the on-winding thermal overload protectors have cooled to anacceptable operating level, the protectors automatically reset and closeto allow the motor 12 to restart. In a particular embodiment of theinvention, the on-winding protectors are Klixon® 7 AM031 or 7 AM036protectors, although others may be used as well.

Another type of protector that may be used with both the low speedwinding thermal overload protector 26 and the high speed winding thermaloverload protector 28 is a disc type thermal overload protector that ispositioned in the end shield of the motor shell 24 and is connected toall three phases of the stator windings as shown for example with thehigh speed stator windings 22 in FIG. 4. The disc type of thermaloverload protector may be a phenolic disc type protector, and in anexemplary embodiment, is a Klixon® MWJ series protector with a ¾″bimetallic snap acting disc on which the contacts for the three phasesof the stator windings are mounted and through which current flows. Ifthe stator windings overheat for any of the reasons discussed above, theheating effect of the current flow through the disc causes the disctemperature to rise. When the disc temperature reaches its calibratedset point temperature, it snaps open and disconnects the current to thestator windings. When the windings and hence the disc has cooled to anacceptable operating level, the phenolic disc protector automaticallyresets and closes to allow the motor 12 to restart. In practice, thephenolic disc may include other series or families of protectors fromKlixon® or other manufacturers or vendors.

The motor controller 14 provides power to and controls operation of theelectric motor 12. As shown in FIG. 1, the motor controller 14 mayreceive power from a single phase AC supply voltage at 115 VAC suppliedby connections L1 and N, where L1 represents the “hot” side of the ACsupply and N represents neutral, which is typically at earth potential.The AC supply voltage may also be 230 VAC, in which case the neutralline would be replaced with another hot supply line. The AC supplyvoltage may also be three phase 480 VAC.

The motor controller 14 may include any combination of circuitry,hardware, firmware, and/or software. In one particular embodiment, themotor controller 14 includes a custom application specific integratedcircuit (ASIC) with a microprocessor that controls and drives a 3-phaseinverter that provides a three phase driving waveform to the low speedcoils 20 and high speed coils 22 of the stator 18. The motor controller14 may also include various other electronic components.

The motor controller 14 may receive commands or operating instructionsfrom one or more controls 30 such as a keypad, switches, or buttons asare commonly found on HVAC systems and other devices. The controls 30may be one or more separate components or may be integrated in the motorcontroller 14.

The above-described invention offers numerous advantages. For example,by using relatively smaller on-winding type protectors on the low speedwindings 20 and a relatively larger phenolic disc type protector only onthe high speed windings 22, the motor casing 24 can be smaller becauseit only has to accommodate one phenolic disc type protector. The presentinvention also reduces the overall cost of the motor 12 because a lessexpensive on-winding protector 26 is used for the low speed statorwindings 22.

Although the invention has been described with reference to thepreferred embodiment illustrated in the attached drawing figures, it isnoted that equivalents may be employed and substitutions made hereinwithout departing from the scope of the invention as recited in theclaims. For example, the specific motor ratings, sizes, etc. disclosedherein can be altered without limiting the scope of the intention.

Having thus described the preferred embodiment of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:

The invention claimed is:
 1. A motor assembly comprising: a motorcontroller; and a three-phase electric motor driven by the motorcontroller and comprising: a stator including three low speedthree-phase windings and three high speed three-phase windings; a rotorrotatably coupled with the stator; three on-winding non-phenolic bimetalsnap-action thermal overload protectors each coupled with a differentone of the three low speed three-phase windings, the three on-windingnon-phenolic bimetal snap-action thermal overload protectors beingconfigured to protect all three phases of the low speed three-phasewindings; a single phenolic bimetal snap-action disc type thermaloverload protector coupled with all three of the high speed three-phasewindings and configured to protect all three phases of the high speedthree-phase windings, the single phenolic bimetal snap-action disc typethermal overload protector being electrically isolated from the threeon-winding non-phenolic bimetal snap-action thermal overload protectors;and a motor shell that partially encloses and protects the stator andthe rotor, wherein the three on-winding non-phenolic bimetal snap-actionthermal overload protectors are wired directly to the low speedthree-phase windings and the single bimetal snap-action disc typethermal overload protector is positioned outside the stator.